This invention relates to an improved azeotropic solvent drying and cleaning system which include a volatile solvent that has a capability of removing water, hydrophilic residues or other films from the surface of substrates and a novel apparatus and method. Removal of the hydrophilic and water containing residues from the substrate surface to be cleaned is effected by displacement or dissolution; cleaning in this manner avoids multi-stage cleaning and drying steps and, in the case of metals, avoids potential corrosion of the kind that results when aqueous cleaning methods are used.
A variety of lubricants, including the conventional petroleum oil type, the water soluble oils and the synthetic or semisynthetic fluids are employed in metal working. Some of these fluids pose a difficult problem when attempts are made to completely cleanse and dry and free the surface of such materials. Vapor degreasers using chlorinated solvents such as 1,1,1-trichloroethane, trichloroethylene, perchloroethylene or methylene chloride are common methods of cleaning metal and other non-absorbent surfaces and work effectively on surface films that are hydrophylic and are typically comprised of oil, water surfactants, metal salts and the like. However, these chlorinated solvents frequently break down and form corrosive hydrochloric acid in the presence of water. Also, many cleaning schemes are not designed to remove water as well as cleaning the surface, a problem that is especially acute when water-extendable metalworking fluids are to be cleaned in a vapor degreaser with a chlorinated solvent.
While the problems resulting from handling water contaminated cleaning fluid could be alleviated by placing only dried or non-water heated parts in the degreaser, this option is not practical especially because a dry film present on an article is often difficult to remove satisfactorily. Also, the elapsed time required to allow parts to dry increases the work-in-process inventory. Requiring parts to sit prior to cleaning increases handling, lowers productivity and reduces manufacturing flexibility.
In my U.S. Pat. Nos. 3,559,297; 2,589,023 and 3,710,450, systems were disclosed for removing water films from cleaned substrates. The present invention deals with a system for the treatment of substrates which are contaminated and require cleansing as well as drying; the operation being effected by a single cleansing/drying system.
It is thus apparent that a need exists for an effective solvent surface cleaning and drying system and, particularly, a system which is readily renewable by separating the water and accumulated surface contaminants therein during use of the solvent without encountering substantial interference by the build up of water and contaminants in the solvent.